Although there is a general consensus on the distribution and ecological features of terrestrial biomes, the allocation of alpine ecosystems in the global biogeographic system is still unclear. Here, we delineate a global map of alpine areas above the treeline by modelling regional treeline elevation at 30 m resolution, using global forest cover data and quantile regression. We then used global datasets to 1) assess the climatic characteristics of alpine ecosystems using principal component analysis, 2) define bioclimatic groups by an optimized cluster analysis and 3) evaluate patterns of primary productivity based on the normalized difference vegetation index. As defined here, alpine biomes cover 3.56 Mkm² or 2.64% of land outside Antarctica. Despite temperature differences across latitude, these ecosystems converge below a sharp threshold of 5.9°C and towards the colder end of the global climatic space. Below that temperature threshold, alpine ecosystems are influenced by a latitudinal gradient of mean annual temperature and they are climatically differentiated by seasonality and continentality. This gradient delineates a climatic envelope of global alpine biomes around temperate, boreal and tundra biomes as defined in Whittaker's scheme. Although alpine biomes are similarly dominated by poorly vegetated areas, world ecoregions show strong differences in the productivity of their alpine belt irrespectively of major climate zones. These results suggest that vegetation structure and function of alpine ecosystems are driven by regional and local contingencies in addition to macroclimatic factors.

中文翻译：

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高山生物群落的全球分布和生物气候特征

尽管就陆地生物群落的分布和生态特征达成了普遍共识，但全球生物地理系统中高山生态系统的分配仍不清楚。在这里，我们通过使用全球森林覆盖率数据和分位数回归，以30 m分辨率对区域树线海拔进行建模，在树线上方绘制了高山区域的全球地图。然后，我们使用全球数据集来进行以下分析：1）使用主成分分析评估高山生态系统的气候特征； 2）通过优化的聚类分析确定生物气候群体； 3）根据归一化的植被指数评估初级生产力的模式。根据此处的定义，高山生物群落覆盖3.56 Mkm ²或南极洲以外土地的2.64％。尽管纬度之间存在温度差异，但这些生态系统仍在5.9°C的临界阈值以下收敛，并趋向于全球气候空间的较冷端。低于该温度阈值，高山生态系统会受到年平均温度的纬度梯度的影响，并且会因季节和大陆性而在气候上有所区别。这个梯度描绘了惠特克（Whittaker）计划中定义的围绕温带，寒带和苔原生物群系的全球高山生物群系的气候范围。尽管高山生物群系同样以植被差的地区为主，但世界经济区无论主要气候区如何，其高山带生产力都存在很大差异。